1. Field of the Invention
The present invention relates to a seat occupant detection apparatus and, more particularly, to a seat occupant detection apparatus that is suitable to accurately detect a load of a seated occupant without involving a reduction in the mounting strength of a seat of a vehicle.
2. Description of the Related Art
Vehicular seat occupant detection apparatuses have been known, as disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 9-207638. An occupant detection apparatus disclosed in the laid-open patent application has load sensors that are disposed between a vehicle body floor and lower seat rails for guiding a vehicular seat. The load sensors are disposed between the lower seat rails and seat-mounting portions provided on the vehicle body floor, at forward and rearward end portions of the lower seat rails, and are fastened to the seat-mounting portions together with the lower seat rails, by bolts. When an occupant sits on the seat, loads corresponding to the occupant""s weight act on the load sensors. Therefore, based on output signals of the load sensors, the above-described seat occupant detection apparatus is able to detect the presence or absence of an occupant on the seat and the load of the seat occupant.
The load sensors are fastened to the floor together with the lower seat rails as described above. Therefore, if the fastening loads on the lower seat rails are increased, the loads acting on the load sensors when there is no occupant on the seat become greater. In this case, the proportion of a difference between the load value detected by the load sensors when there is no occupant on the seat and the load value detected when there is an occupant on the seat becomes small, so that the precision of occupant load measurement decreases. If the fastening load is reduced in order to avoid the aforementioned drawback, the mounting strength of the seat tracks decreases so that drawbacks, such as occurrence of rattling and the like, may occur.
Furthermore, in the conventional occupant detection apparatus, the load sensors are disposed between the lower seat rails and the vehicle floor as mentioned above. Therefore, when the seat is slid forward or rearward relative to the seat track, the distribution of loads on the forward and rearward load sensors changes. If the amount of slide of the seat becomes great, there may occur an event that pulling loads act on load sensors. In that event, it becomes impossible to accurately detect the load of an occupant by the load sensors.
The disclosure of Japanese Patent Application No. HEI 11-252163 filed on Sep. 6, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
It is an object of the invention to provide a seat occupant detection apparatus capable of accurately detecting the load of a seated occupant without involving a reduction in the mounting strength of a vehicular seat.
In accordance with the invention, a seat occupant detection apparatus comprises a beam member that is displaced in accordance with a load of an occupant seated on a vehicular seat, and load detecting means for detecting the load based on an amount of displacement of the beam member.
In the seat occupant detection apparatus of the invention, the beam member is displaced in accordance with the load of an occupant seated on the vehicular seat. The mounting strength of the beam member at support points does not affect the load-displacement characteristic of the beam member. Therefore, according to the invention, it becomes possible to detect the load of a seated occupant without involving a reduction in the mounting strength of the vehicular seat.
Furthermore, the beam member may be connected between a seat frame and a seat pan of the vehicular seat.
In the above construction, the beam member is connected between the seat frame and the seat pan of the vehicular seat. When the vehicular seat is slid forward or rearward, the seat pan and the seat frame are displaced together with the vehicular seat. Therefore, the distribution of loads inputted to the beam member does not change regardless of the slide position of the vehicular seat. Therefore, according to the invention, it becomes possible to more accurately detect the load of a seated occupant without being affected by the slide position of the vehicular seat.
Furthermore, the beam member may be connected, at first mounting positions provided near opposite end portions of the beam member, to one of the seat pan and the seat frame, and the beam member may be connected to another one of the seat pan and the seat frame, at second mounting positions that are positioned at a predetermined distance inward from the first mounting positions on the beam member.
Furthermore, the beam member may be an elastic member having a predetermined flexural rigidity, and the load detecting means may detect the load based on a flexure of the beam member.
Furthermore, the beam member may be an elastic member having a predetermined flexural rigidity, and the load detecting means may detect the load based on an amount of flexure of a substantially middle portion of the beam member in a direction of a length of the beam member.
In the above construction, at first mounting positions provided near opposite end portions of the beam member, to one of the seat pan and the seat frame, and the beam member is connected to the other one of the seat pan and the seat frame, at second mounting positions that are positioned at a predetermined distance inward from the first mounting positions on the beam member. The beam member is supported at the mounting points of the seat frame, and the load of a seated occupant is inputted to the mounting points of the seat pan. That is, in the beam member, one group of the first mounting positions and the second mounting positions become fulcrums, and the other group of mounting positions become load input points. The beam member is an elastic member having a predetermined flexural rigidity, and the load of a seated occupant is detected based on the amount of flexure of a substantially middle portion of the beam member. In this construction, the effect that a change of the distribution of loads inputted to the two load input points has on the amount of flexure of the middle portion of the beam member is small. Therefore, according to the invention, it becomes possible to detect the load of a seated occupant with a high precision even if the seated position of the occupant changes.
Furthermore, the seat occupant detection apparatus may further include a strain amplifying mechanism that amplifies a strain associated with the flexure of the beam member, and the load detecting means may detect the load based on the strain amplified by the strain amplifying mechanism.
According to the above construction, the provision of the strain amplifying mechanism for amplifying the strain associated with the flexure of the beam member having an elasticity makes it possible to detect the flexure of the beam member, that is, the load of a seated occupant, with a higher precision.
Furthermore, the strain amplifying mechanism may include a second elastic beam member that is supported by one of the seat pan and the seat frame and that has a length that is less than a length of the beam member, and a transmission member that transmits the flexure of the beam member to the second elastic beam member, wherein the load detecting means detects the load based on the strain of the second elastic beam member.
In the above construction, the flexure of the beam member is transmitted to the second elastic beam member. The second beam member has a less length than the beam member. In general, if the flexure of a beam member is constant, the magnitude of strain that occurs in association with the flexure is inversely proportional to the square of the length of the beam member. Therefore, according to the invention, the second elastic beam member is caused to have a strain that is greater than a strain that occurs in the beam member.
Furthermore, the strain amplifying mechanism may be a small-section modulus portion provided by forming a portion of the beam member so that a section modulus of the portion with respect to a neutral axis of the portion is less than the section modulus of another site of the beam member, and the load detecting means may detect the load based on the strain of the small-section modulus portion.
In the above construction, the beam member is provided with a small-section modulus portion that has a smaller section modulus with respect to the neutral axis than other sites of the beam member. In general, if the bending moment that occurs to the beam member is constant, the strain that occurs on a surface of the beam member is inversely proportional to the section modulus. Therefore, the small-section modulus portion of the beam member receives greater strain than other sites of the beam member.
Furthermore, the small-section modulus portion may be formed by making a section of a portion of the beam member smaller than a section of another site of the beam member.
Furthermore, the beam member may be substantially a rigid body and may be pivotably connected to the seat pan and the seat frame.
In the above construction, since the beam member is substantially a rigid body, the beam member pivots in accordance with a load that is inputted to the beam member. Therefore, it becomes possible to detect the load of a seated occupant in accordance with the amount of pivot of the beam member.
Furthermore, the seat occupant detection apparatus may further include an elastic member that elastically deforms in accordance with a pivot of the beam member, and the load detecting means may detect the load based on an amount of elastic deformation of the elastic member.
In the above construction, the load of a seated occupant is detected based on the amount of elastic deformation of the elastic member that elastically deforms in accordance with the pivot of the rigid beam member. Therefore, the load measurement precision is dependent only on the elastic characteristics of the elastic member, and is not affected by the mechanical characteristics of the beam member. Hence, the quality control of the component parts becomes easier.